JP3513934B2 - Exhaust gas purification catalyst and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying catalyst for purifying NOx in exhaust gas of an automobile engine and the like, and a method for producing the same.

[0002]

2. Description of the Related Art An exhaust gas purifying catalyst for purifying NOx (nitrogen oxide) in exhaust gas is selected from hydroxides, carbonates, and bicarbonates of alkali metals or alkaline earth metals. At least one (component (a)), Pt, N
It is known that zeolite has a carrier of a transition metal such as i and at least one kind of oxide or halide thereof (component (b)) supported thereon (see Japanese Patent Laid-Open No. 4-197447). This exhaust gas purifying catalyst is prepared by, for example, immersing zeolite in an aqueous solution in which platinum chloride hexahydrate is dissolved, pulling it up and heating and drying it, and then immersing it in an aqueous solution of lithium hydroxide or the like, pulling it up and heating and drying It is manufactured by the method.

[0003]

The above-mentioned prior art is (a)
Increases the absorption of NOx in the exhaust gas by the component, (b)
Although it is intended to decompose the NOx by a component, the object of the present invention is to increase the NOx purification rate by using a noble metal and NiO in combination, and further increase the heat resistance of the catalyst.

That is, when the present inventor supports Pt on the main catalyst and Ni on the co-catalyst on the zeolite, Ni slightly reduces the activity of Pt in the range where the amount of Ni supported is small, thereby increasing the NOx purification rate. It was confirmed by experiments that the activation temperature of the catalyst can be shifted to the high temperature side without lowering it. However, there is a problem that the NOx purification rate is greatly reduced when the amount of Ni carried is increased. Then, this problem becomes particularly remarkable when the amount of HC in the exhaust gas is small.

Pt is supported on zeolite and N
In the case of supporting i, the Pt-supported zeolite has N
The i solution is usually impregnated. However, according to this method, since the Ni solution adheres to the entire Pt-supported zeolite, Ni is changed into NiO by the subsequent firing or the heat of the high-temperature exhaust gas to form a NiO film. The NiO film covers the active site (Pt) of the catalyst, and
The membrane will block the gas passages (pores and mesopores of zeolite). Therefore, even if Ni itself is originally useful as a co-catalyst, as described above, Ni changes to NiO to cover the active site of the catalyst and crush it, and further block the gas passage to prevent passage or adsorption of HC. It is considered that the secondary adverse effect of being disturbed causes a large decrease in the NOx purification rate.

[0006]

Therefore, in the present invention, Ni is not impregnated and supported on a crystalline metal-containing silicate having pores such as zeolite in the form of a Ni solution, but is oxidized. By supporting the catalyst in the form of nickel powder, Ni can be effectively used for improving the activity and heat resistance of the catalyst while securing the active points of the catalyst and preventing the gas passages from being blocked. It is the one. Hereinafter, the invention according to each claim will be specifically described.

<Invention of Claim 1> This invention relates to a crystalline metal-containing silicate and a catalytic noble metal.
And NO in the exhaust gas.
An exhaust gas purifying catalyst that decomposes x in the presence of HC, containing a metal in which the above catalytic noble metal is supported on a monolith carrier.
A silicate coat layer is formed and has the above coat layer.
A monolith carrier that converts nickel oxide powder into ion-exchanged water
The nickel oxide powder is dipped in the slurry to be added.
Is supported on the above metal-containing silicate,
The weight ratio of Ni to the contained silicate is from 2/100 to
It is characterized by being 51/100 .

In the case of the present invention, since Ni is supported on the metal-containing silicate in the form of nickel oxide powder, even if there are places where the nickel oxide powder is densely distributed on the metal-containing silicate, that powder Since there is a gap between them, HC and NOx in the exhaust gas can reach the active site of the catalyst through the gap, and also pass through the gap to the pores and mesopores of the metal-containing silicate. Can be reached That is, the nickel oxide powder,
It does not cover the active site of the catalyst so that HC or NOx cannot reach it, or does not completely block the gas passage, but on the contrary, enhances the activity of the catalyst by interacting with the precious metal, which is the main catalyst metal, and Thus, it effectively functions as a co-catalyst that suppresses thermal deterioration (for example, sintering) of the catalytic metal.

The metal-containing silicate may be an aluminosilicate (zeolite) using Al as a metal forming a crystal skeleton (crystal lattice), but instead of Al or together with Al, Ga, Ce, Mn, Tb. It may be a metal-containing silicate using other metal such as skeleton. As zeolite, type A, type X, type Y,
Any of mordenite, ZSM-5, etc. may be used. Also,
The type of the catalyst metal is also not particularly limited, and noble metals such as Pt, Ir, and Rh can be used alone or in combination.

In the present invention, the weight ratio of Ni is 2
/ 100 or more is because the effect of supporting the nickel oxide powder on the metal-containing silicate becomes clear by this, and the Ni weight ratio is 51/100.
The following is because even if it is difficult to close the gas passage of the metal-containing silicate in the case of nickel oxide powder, it will be blocked to some extent, so if the amount of the nickel oxide powder becomes excessive,
This is because it becomes disadvantageous in terms of purification of exhaust gas.
From such a viewpoint, a more preferable range of the weight ratio of Ni is 5/100 to 46/100.

<Invention of Claim 2 > The present invention is a method for producing an exhaust gas purifying catalyst in which a noble metal and nickel oxide powder are carried on a crystalline metal-containing silicate, wherein the noble metal is contained on the metal-containing silicate. Is carried out, and the metal-containing silicate is carried on the monolith carrier by washcoating, and thereafter, the nickel oxide powder is carried on the monolith carrier by washcoating to carry the nickel oxide powder on the metal-containing silicate. .

In the present invention, the noble metal is first loaded on the metal-containing silicate, and the nickel oxide powder is subsequently loaded on the metal-containing silicate. Therefore, the same action as that of the third aspect of the invention can be obtained. After washcoating the metal-containing silicate carrying the monolith carrier on the monolith carrier, since the nickel oxide powder is washcoated onto the monolith carrier, the metal-containing silicate is compared to the case where the metal-containing silicate and the nickel oxide powder are simultaneously washcoated on the monolith carrier. Thus, the nickel oxide powder can be surely supported.

[0013]

According to the invention of claim 1, the monolith
A coating of metal-containing silicate in which a catalytic noble metal is supported on a carrier.
Formed with a coating layer, and the monolith carrier having the coating layer
Is a slurry made by adding nickel oxide powder to ion-exchanged water.
And the nickel oxide powder contains the above metal.
Supported on silicate, the above metal-containing silicate
The weight ratio of Ni to 2/100 to 51/100
Because there, without interfering with the catalytic function of the metal-containing silicate and precious metals, it is possible to effectively utilize the nickel oxide as a co-catalyst, it is possible to improve the heat resistance of the NOx purification rate and catalyst.

According to the second aspect of the present invention, the metal-containing silicate is loaded with the noble metal, the metal-containing silicate is loaded on the monolith carrier by washcoating, and then the monolithic carrier is washcoated with nickel oxide powder. Since the nickel oxide powder is supported on the metal-containing silicate by the above, the same effect as that of the invention according to claim 3 can be obtained, and the nickel oxide powder can be surely supported on the metal-containing silicate. it can.

[0015]

EXAMPLES Examples of the present invention will be described below.

(Preparation of Exhaust Gas Purifying Catalyst of Example) Pt and Rh were used as catalyst metals in a weight ratio of Pt: Rh.
= 75: 1 and 4.5 g per liter of catalyst, and this was weighed by a spray dry method to obtain H-type ZSM5 (SiO ₂ / A) as a metal-containing silicate.
L ₂ O ₃ = 80) and further heat-treated at 300 ° C. to obtain a main catalyst powder. Then, 20 parts of hydrated alumina was used as a binder in the main catalyst powder.
wt% was added, and further an appropriate amount of water was added to obtain a slurry for washcoat. A cordierite honeycomb carrier was dipped in this slurry, pulled up to blow off excess slurry, and then the coat layer was dried.

Next, NiO powder was added to ion-exchanged water, and a binder (alumina) in an amount of 1/10 the weight of NiO powder was added to obtain a washcoat slurry. The honeycomb carrier was immersed in this slurry, pulled up to blow off excess slurry, and then fired at 500 ° C. for 2 hours in the atmosphere to obtain a desired honeycomb catalyst. In this case, N
The amount of iO is converted to the amount of Ni and is 25/10 of H type ZSM5.
It was adjusted to be 0 (weight ratio).

(Preparation of Exhaust Gas Purifying Catalyst of Comparative Example) The above-mentioned main catalyst powder was carried on a similar honeycomb carrier by wash coating and fired at 500 ° C. for 2 hours to obtain a honeycomb catalyst of Comparative Example 1. It was

A comparative example was also prepared by supporting the above-mentioned main catalyst powder on a similar honeycomb carrier by wash coating, impregnating this with an aqueous solution of nickel nitrate, sufficiently drying and then calcining at 500 ° C. for 2 hours. Two
A honeycomb catalyst of was obtained. The amount of Ni in this catalyst is 25/100 (weight ratio) of H-type ZSM5 as in the case of the above-mentioned examples.

(Evaluation 1 of Catalyst) The NOx purification rate of each of the honeycomb catalysts of the above Examples and Comparative Examples 1 and 2 was measured under the following conditions.
The results shown in are obtained.

-Measurement conditions-Gas composition HC; 500 ppm C, O ₂ ; 7%, NOx; 250 p
pm, rest N ₂ space velocity (SV) 55000h ^-1

According to FIG. 1, in the example in which the NiO powder was carried, the peak value of the NOx purification rate (catalyst inlet temperature 20
(Appearing near 0 ° C.) is higher than in Comparative Example 1 in which Ni is not supported. On the other hand, in the case of the comparative example 2, the same amount of Ni as that of the example is carried, but the NOx purification rate is considerably low. The NOx purification rate of Comparative Example 2 is low because the N-impregnated and supported on the H-type ZSM5.
It is considered that this is because the i salt was changed to NiO by the subsequent firing, the active sites were crushed, and the gas passage of the H-type ZSM5 was blocked. As in the example, Ni was supported on the H-type ZSM5 in the form of NiO powder. It can be seen that this is effective in increasing the NOx purification rate.

(Catalyst Evaluation 2) Next, for each of the honeycomb catalysts of the above-mentioned Example and Comparative Example 1, after subjecting them to heat treatment at 900 ° C. for 50 hours, the NOx purification rate was measured under the following conditions. , Fig. 2
The results shown in are obtained.

[0024] - Measurement conditions - the gas composition _{HC; 4000ppmC, O 2; 7} %, NOx; 250
ppm, CO; 0.15%, balance N ₂ space velocity (SV) 55000h ^-1

According to FIG. 2, the NOx purification rate in the example is higher than that in the comparative example 1 in the entire temperature range.
It can be seen that supporting O powder is effective for improving heat resistance.

(Catalyst Evaluation 3) Fulbrick (gorgerite 1.3 liter honeycomb carrier) in the same manner as in the above Examples and Comparative Examples 1 and 2.
A catalyst was prepared, and by a bench on the bench (an automobile engine was fixedly operated on the bench and the exhaust gas was passed through the catalyst), the NOx purification rate under the conditions of A / F = 22 and catalyst inlet gas temperature of 280 ° C. Was measured. The results are shown in Table 1. Each catalyst was not subjected to the heat treatment performed in Evaluation 2 above.

[0027]

[Table 1]

According to the above table, when the amount of HC discharged from the engine is large (2000 ppmC), Ni
The NOx purification rate of the example supporting Comparative Example 2 and the comparative example 2 is higher than that of the Comparative Example supporting no Ni. Comparative example 2
The NOx purification rate is high because the formation of the NiO film partially closes the gas passage.
It is recognized that there is no shortage of HC due to the large amount of C. This means that when the amount of HC is small (50
This is supported by the fact that the NOx purification rate of Comparative Example 2 is low at 0 ppmC.

On the other hand, the examples show a high NOx purification rate even when the amount of HC is small at 500 ppmC. From this fact as well, the fact that Ni is supported on the metal-containing silicate in the form of NiO powder is It can be seen that there is no blockage of the gas passage, and it is extremely effective in improving the NOx purification rate.

(Regarding Ni Content) Eight kinds of honeycomb catalysts having different Ni contents were prepared in the same manner as in the above-mentioned example, and the catalyst inlet gas temperature was set to 250 ° C. under the same conditions as in the evaluation 1 described above. After fixing, each NOx purification rate was measured. The result is as shown in FIG.

According to FIG. 3, the NOx purification rate increases as the amount of Ni increases.
The purification rate is decreasing. It is considered that this is because when Ni is supported in the form of NiO on the metal-containing silicate, the problem of gas passage clogging is small, but when NiO is excessive, the problem of gas passage clogging occurs. From the figure, in order to secure the NOx purification rate of 27% or more, the amount of Ni should be 2
/ 100 to 51/100, and further N
To secure an Ox purification rate of 30% or more, the Ni content should be 5/10.
It can be seen that it may be set to 0 to 46/100.

In loading the catalyst metal on the metal-containing silicate, a method of supporting the catalyst metal on the metal-containing silicate by hydrolysis can be adopted.
As a result, the catalyst metal can be highly dispersed to prevent sintering due to the heat of the catalyst metal, that is, the heat resistance of the catalyst can be improved.

[Brief description of drawings]

FIG. 1 is a NO at the time of freshness in Examples and Comparative Examples 1 and 2.
x Graph showing purification characteristics

FIG. 2 is a graph showing NOx purification characteristics after heat treatment in Examples and Comparative Examples.

FIG. 3 is a graph showing the relationship between the amount of Ni and the NOx purification rate.

[Explanation of symbols]

None

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-5-317720 (JP, A) JP-A-6-1006065 (JP, A) JP-A-5-253488 (JP, A) JP-A-2- 157042 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) B01J 21/00-38/74 B01D 53/94

Claims (2)

(57) [Claims] 1. A noble metal catalyst for a crystalline metal-containing silicate.
The genus and nickel oxide are supported, and N in the exhaust gas
In an exhaust gas purifying catalyst for decomposing Ox in the presence of HC, a metal-containing silicium having a monolithic carrier carrying the above-mentioned catalytic noble metal.
A coating layer of silicate is formed, and the monolith carrier having the coating layer is nickel oxide powder.
Immersed in a slurry of powder added to ion-exchanged water,
The nickel oxide powder is supported on the metal-containing silicate.
And the weight ratio of Ni to the metal-containing silicate is 2 /
100-51 / 100 Exhaust gas purification catalyst characterized by the above-mentioned. 2. A method for producing an exhaust gas purifying catalyst in which a noble metal and nickel oxide powder are carried on a crystalline metal-containing silicate, wherein the noble metal is carried on the metal-containing silicate, and the metal-containing silicate is a monolith. A method for producing an exhaust gas purifying catalyst, characterized in that the carrier is supported by wash coating, and then the nickel oxide powder is wash coated on the monolith carrier to support the nickel oxide powder on the metal-containing silicate.